Many governmental entities are now requiring handheld telephony devices to include user adjustable features for disabled or handicapped employees, such as the hearing impaired. Section 508 of the Workforce Investment Act of 1998, for example, is intended to make communication systems accessible to hearing impaired employees of the U.S. government. The Act imposes mandatory procurement requirements on the government. Two such requirements are:
(i) for transmitted voice signals, telecommunications products shall provide a gain adjustable up to a minimum of 20 db and, for incremental volume control, at least one intermediate step of 12 db of gain shall be provided; and
(ii) if the telecommunications product allows a user to adjust the receive volume, a function shall be provided to automatically reset the volume to the default level after every use.
Existing handheld telecommunication devices are generally noncompliant with these provisions. For example, the typical office telephone offers a maximum gain of 12 dB. The typical residential telephone offers no ability to adjust the gain. Even on telephones that permit the gain to be adjusted by the user, automatic post-call reset to a default level is generally not provided.
No new technologies would be required to design and build telecommunication devices, such as telephones, that provide the desired capabilities. The engineering challenge is to find an economical way to bring existing telecommunication devices and systems into compliance.
One obvious way to provide 20 dB of gain, with automatic post-call reset, is to boost the output of the private Branch Exchange (PBX), Central Office Switch, or other centralized device that is serving a plurality of users. What makes this approach impractical is that standard encoding and transmission algorithms, such as 64-Kilobit Pulse Code Modulation or 13.2-Kilobit GSM, do not have 20 dB of “headroom” available. Attempts to boost transmission gain by more than 12 dB often results in unacceptable distortion, similar to what is experienced when an inexpensive radio is turned up too loud.
The other obvious solution is to upgrade the amplifiers in the endpoint devices themselves, so that they provide 20 dB of gain and automatic post-call reset. Although there are no technical barriers to this approach, the costs of replacing the amplifier modules in existing telephones, coupled with the costs of modifying all existing production lines, make this approach impractical.